Sift the cocoa powder to make sure there are absolutely no clumps. Then pour the cocoa powder into a small saucepot, or microwave-safe bowl.
Add in the sweetened condensed milk, butter, and a pinch of salt.
If using the stovetop method, set the pot over medium-low heat and stir the contents until the butter is fully melted and the cocoa powder is completely combined. The sauce should be very smooth, but thick. Mix in the vanilla extract and then thin out the hot fudge sauce by adding ¼ - ½ cup of milk. Stir to your desired consistency and turn off the heat.
If using the microwave method, place the microwave-safe bowl in the microwave and set on high for 1 minute. Mix the ingredients and microwave again in 30 second increments, stirring in between, until the mixture is very smooth. Then, stir in the vanilla extract, and thin out the sauce by adding ¼ - ½ cup of milk to reach your desired consistency.
Notes
The hot fudge sauce can be stored in an airtight container at room temperature for up to three days, or in the refrigerator for up to 3 weeks.The sauce will thicken when cool, so re-warm it on the stovetop or in the microwave before serving.Alternative Thick Chocolate Sauce Recipe –